c# - EF Core 从列表中动态过滤

Question

我正在努力在前端表上创建一个通用动态过滤器。这个想法是每列都有一个过滤器，您可以在其中选择该列的值。列名必须是完全动态的和选定的值。我们正在使用 .NET 5 和 EF Core 5。

我想要的 SQL 查询是：

SELECT * 
FROM Users
WHERE externalId IN ('1234', '5678');

楷模：

public class ColumnFilter
    {
        [Required]
        public string Name { get; set; } // column name
        public List<string> SelectedValues { get; set; } = new List<string>(); // values selected in this column
    }

public class User {
        public string Name { get; set; } 
        public string ExternalId { get; set; } 
}

简化代码：

//columnfilter really comes from API request
var columnFilter = new ColumnFilter{
Name = "ExternalId",
SelectedValues = new List<string>{ "1234", "5678" }
};

var queryable = _context.Users.AsNoTracking();

queryable = queryable.Where(f => columnFilter.SelectedValues.Contains(EF.Property<string>(f, columnFilter.Name)));

var values = await queryable.ToListAsync(); // 0 results

EF Core 生成此查询：

      SELECT *
      FROM [Users] AS [u]
      WHERE 0 = 1

我如何让它动态工作？

标签： c#asp.netentity-framework.net-coreentity-framework-core

Answer 1

这是一个使用字符串值的示例：

var queryable = _context.Users.AsNoTracking();

queryable = queryable.FilterDynamic(columnFilter.Name, columnFilter.SelectedValues);

public static class QueryableExtensions
{
    public static IQueryable<T> FilterDynamic<T>(this IQueryable<T> query, string fieldName, ICollection<string> values)
    {
        var param = Expression.Parameter(typeof(T), "e");
        var prop = Expression.PropertyOrField(param, fieldName);
        var body = Expression.Call(typeof(Enumerable), "Contains", new[] {typeof(string)},
            Expression.Constant(values), prop);
        var predicate = Expression.Lambda<Func<T, bool>>(body, param);
        return query.Where(predicate);
    }
}